(A) Field of the Invention
The present invention relates to a current sensing circuit and method of a high-speed driving stage, particularly to a current sensing circuit and method of a high-speed driving stage that can largely reduce power consumption.
(B) Description of Related Art
To prevent over-loading in electric circuits with high voltage or current, a current sensing circuit of a driving stage usually needs to be included for detecting abnormal changes in current.
A conventional current sensing circuit of a high-speed driving stage requires connecting a current detecting resistance in the driving stage in series, and then using an operational amplifier to enlarge the voltage of the current detecting resistance and convert it into a current for the subsequent signal processing. For this reason, the prior art current sensing circuit has the following drawbacks:
1. The use of series resistance will increase power consumption and lower efficiency.
2. The use of an operational amplifier will complicate the circuits and slow down the operating speed.
3. The series resistance inside the integrated circuits will fluctuate due to process variation and create errors of detecting current.
Another current sensing circuit is disclosed in U.S. Pat. No. 6,384,636 (referred to xe2x80x9c636 patentxe2x80x9d hereinafter), entitled xe2x80x9cFast and Precise Current-sense Circuit for High-voltage Switch.xe2x80x9d The current sensing circuit of the ""636 patent comprises a first conductive path which is formed by the loading current switch and a second conductive path which is formed by the voltage divider, and an output circuit is used to measure the difference between the output current of the second conductive path and the bias current so as to determine the change of the loading current. However, the ""636 patent requires a three-fold bias current due to the demand of its circuit design so that the power consumption of the ""636 patent will increase. Additionally, the ""636 patent requires the use of differential output mode so as to determine the change of the loading current, so its circuit design is more complicated and takes up more chip space.
In view of the existing problems of the prior art, the present invention hereby sets forth a novel current sensing circuit of a high-speed driving stage with a view to overcome the drawbacks mentioned above.
The main object of the present invention is to provide a current sensing circuit and method of a high-speed driving stage which are suitable for use in sensing circuits with low power consumption.
The current sensing circuit of a high-speed driving stage disclosed in the present invention is capable of linearly detecting the output current of the driving stage transistors, and directly condensing the detected current to an appropriate value using the geometric ratio of the transistors, so as to facilitate the subsequent signal processing circuit to use it for control purposes.
To achieve the above-mentioned objects, the current sensing circuit of a high-speed driving stage disclosed in the present invention comprises an input stage, a level converting unit, a feedback unit, a current mirror unit, and a current shunting unit. The input stage is used for controlling the synchronization of start-up and shut-off with the high-speed driving stage, and the level converting unit is used for converting the output voltage of the input stage. The feedback unit is used for converting the output voltage of the level converting unit into a current, and the current mirror unit is used for generating an output current that is proportioned to the feedback unit. The current shunting unit is used for shunting the output current of the current mirror unit, while generating a current that is proportional to the current of the high-speed driving stage.
The current sensing circuit of a high-speed driving stage of the present invention includes steps (a) to (d). In step (a), the output voltage of the high-speed driving stage is retrieved. In step (b), the output voltage level of the high-speed driving stage is adjusted by resistors and the first current source. In step (c), the voltage level is converted into a reference current by a feedback unit. In step (d), an output current is shunted from the reference current, wherein the output current is in direct proportion to the output current of the high-speed driving stage and the dimension ratio between the resistor and the transistor of the high-speed driving stage.
The present invention also allows the use of differential output mode, which, however, makes the circuit design more complicated and takes up more chip space. Furthermore, the transistors of the present invention can also be replaced with resistors that can function just as well with equivalent effects.